According to the Find documentation, indexing objects from outside of Episerver is supported. But you need to do the indexing yourself (e.g. on an event or in a scheduled job), loading the entities from your database and batch index them through the Find API. There are small code samples on that documentation page.

Working with Find is easier than Solr and you will end up having a single consolidated search solution. I cannot see why this would not be a good decision.

Worth noting that Episerver Find is built upon Elastic search which is a generic search solution. So Episerver Find has plenty of power in this area if needed. But you will need to configure the indexing and search a little by yourself unlike for Episerver content that is setup to work automagically.